A malady in which one involuntarily remembers images and snippets of conversation from the previous night's activities.
ie, The egg slipped off his fork, as he remembered how the tall girl had rolled her eyes at him outside the bar the night before. In addition to a throbbing headache, John had woken up with a vicious case of the morning birds.
Used to mean the first day of a the woman's menstrual cycle. Can be metaphorical to the morning of December the 25th, because one awakens to view giant red packages under the tree, or bush.